Solid free-form fabrication (SFF) is a designation for a group of processes that produce three dimensional shapes from additive formation steps. SFF does not implement any part-specific tooling. Instead, a three dimensional component is often produced from a graphical representation devised using computer-aided modeling (CAM). This computer representation may be, for example, a layer-by-layer slicing of the component shape into consecutive two dimensional layers, which can then be fed to control equipment to fabricate the part or repair the part. Alternatively, the process may be user controlled instead of computer controlled. Generally speaking, a component may be manufactured or repaired using SFF by successively building feedstock layers representing successive cross-sectional component slices. Although there are numerous SFF systems that use different components and feedstock materials to build or repair a component, SFF systems can be broadly described as having an automated platform/positioner for receiving and supporting the feedstock layers during the process, a feedstock supplying apparatus that directs the feedstock material to a predetermined region to build the feedstock layers, and an energy source directed toward the predetermined region. The energy from the energy source modifies the feedstock in a layer-by-layer fashion in the predetermined region to thereby manufacture or repair the component as the successive layers are built onto each other.
One recent implementation of SFF is generally referred to as ion fusion formation (IFF). With IFF, a torch such as a plasma, gas tungsten arc, plasma arc welding, or other torch with a variable orifice is incorporated in conjunction with a stock feeding mechanism to direct molten feedstock to a targeted surface such as a base substrate or an in-process structure of previously-deposited feedstock. A component is built using IFF by applying small amounts of molten material only where needed in a plurality of deposition steps, resulting in net-shape or near-net-shape parts without the use of machining, molds, or mandrels. The deposition steps are typically performed in a layer-by-layer fashion wherein slices are taken through a three dimensional electronic model by a computer program. A positioner then directs the molten feedstock across each layer at a prescribed thickness.
There are also several other SFF process that may be used to manufacture or repair a component. Direct metal deposition, layer additive processes, and selective laser sintering are just a few SFF processes. U.S. Pat. No. 6,680,456, discloses a selective laser sintering process that involves selectively depositing a material such as a laser-melted powdered material onto a substrate to form complex, net-shape objects. In operation, a powdered material feeder provides a uniform and continuous flow of a measured amount of powdered material to a delivery system. The delivery system directs the powdered material toward a deposition stage in a converging conical pattern, the apex of which intersects the focal plane produced by a laser in close proximity to the deposition stage. Consequently, a substantial portion of the powdered material melts and is deposited on the deposition stage surface. By causing the deposition stage to move relative to the melt zone, layers of molten powdered material are deposited. Initially, a layer is deposited directly on the deposition stage. Thereafter, subsequent layers are deposited on previous layers until the desired three-dimensional object is formed as a net-shape or near net-shape object. Other suitable SFF techniques include stereolithography processes in which a UV laser is used to selectively cure a liquid plastic resin.
One inherent challenge that presents when using SFF, and more particularly an IFF process, to repair a component is with the positioning system. The positioning system generally serves to position a workpiece, so that operations can be performed on it by adding additional material through a wire or powder feed mechanism, referred to herein as a feedstock feed mechanism, at a deposition point. The positioning system may coordinatingly control all three participants of the workpiece manufacturing process, namely the workpiece, the feedstock feed mechanism, and the plasma welding torch. In this way, three-dimensional articles can be fabricated in a predictable, highly-selectable, and useful manner. Control of the positioning system may be achieved manually, by computer-implemented control software, or the like.
Many times when repairing a component using an SFF process the location of the component to be prepared presents a challenge. In many instances the positioning system becomes too large to bring it to the component to be repaired, such as when the part resides inside the hull of a ship. Similarly, many times the component to be repaired is too large to bring it to the system to be repaired, such as when a large diameter pipe is in need of repair. Hence, there is a need for an IFF process and positioning system that provides customization of the system to enable the system to be positioned relative to the component for repair when it is inaccessible with a typical positioning system.